Operation of liquid-metal-cooled fast breeder reactors results in production of radioactive sodium waste material or radioactive sodium and potassium waste material, depending on the liquid coolant used in the reactor. The sources of this radioactive alkali metal include cold-trap disposal, maintenance operations, and fuel-reloading operations. At the end of the useful life of the plant, the entire alkali metal waste of the plant must be handled in such a way as to minimize its impact on the environment and to minimize cost. Any alkali metal that has been exposed to the breeder reactor core for a significant time must be carefully handled and controlled because of its fission-product and activation-product content. Among the options available for disposal of this radioactive alkali metal, the most promising are: (1) disposal in a permanent repository, (2) disposal in a landfill burial site, and (3) reuse in a new breeder reactor. The choices among these options depend on the activity level, the presence or absence of transuranics, and the quantity of alkali metal involved. The first cited option could be suitable for small quantities of alkali metal containing transuranics; the second cited option is available for small quantities of alkali metal with low level radioactivity but without transuranics; and the third cited option is available for large quantities of alkali metal.
Large quantities of alkali metal that have become contaminated by means of significant fuel-coolant interaction could be reused if the alkali metal were decontaminated. In any decontamination operation, such as reflux distillation, a small volume of highly radioactive contaminated alkali metal remains in the original alkali metal treated. This small quantity of highly radioactive alkali metal could then be disposed of in a permanent repository.
In order to prevent the alkali metal from interacting with the environment, final disposal must be in a form stable to the environment such as certain non-metallic compounds. Various types of glasses containing silica and alkali monoxides may be suitable as the stable form for permanent repository. For example, the composition of ordinary window glass is 17% by weight sodium monoxide, 6% by weight calcium oxide, 1% by weight aluminum oxide with he balance being silica. The volume of this glass made from a given mass of elemental sodium is approximately 3 times the original volume of the sodium metal, but this expansion in volume of waste material is not unacceptable in view of the benefits derived from the product.
While typical or ordinary window glass is not ideal for disposal of radioactive sodium, or radioactive potassium or mixtures of sodium and potassium, from the standpoint of leaching of the fission products by water, other glass compositions are suitable as candidate materials for encapsulation of high-level waste from breeder reactors or for that matter from fuel-reprocessing. These glasses typically contain both silica and sodium or potassium monoxide in various silicon to alkali metal ratios. Additive oxides which may be compounded with the radioactive alkali metal monoxide and the silica generally are selected from the following class of compounds including aluminum, antimony, arsenic, barium, beryllium, boron, calcium, cadmium, germanium, lead, magnesium, phosphorus, silicon, vanadium, zinc and zirconium. However, it has been found that additives selected from the oxides of boron, aluminum, calcium and magnesium are preferred. It has also been found that the use of boron in at least as great a quantity as the sum of the aluminum, calcium and magnesium oxides results in a better leach proof glass.
Representative prior art which relates to the production of glass for the storage of radioactive alkaline waste includes U.S. Pat. No. 4,032,615 issued Jun. 28, 1977 to Johnson, U.S. Pat. No. 4,032,614 issued Jun. 28, 1977 to Lewis, U.S. Pat. No. 4,107,306 issued Apr. 12, 1977 to Batoux et al., U.S. Pat. No. 3,854,933 issued Dec. 17, 1974 to Furakawa et al., and U.S. Pat. No. 2,527,443 issued Oct. 24, 1952 to Padgitt. In addition to the above listed patents, U.S. Pat. No. 4,234,449 issued to Wolson et al., Nov. 18, 1980 also relates to a rotary drum reactor for the two-step production of glass for storing radioactive metal waste, the disclosure of the '449 patent is incorporated herein by reference.